I only see one correct choice among those presented. Here goes:
1. The code will fail to compile If the code fails to compile, none of the other options are viable because they occur only at runtime.
If this code is compiled with the "Enable Assert Keyword" or the like option in your
IDE or with, in some form, the -ea switch at the command line, the code will compile.
If we agree to run this under
Java 1.4 and set the appropriate switches, we can discuss the other choices.
2. Seperate threads can execute the up method concurrently Separate threads cannot execute a synchronized method.
3. Seperate threads can execute the down method concurrently This is true. The down method is not synchronized.
4. Seperate threads can execute both the up and down methods concurrently Apply the && operator to choices 2 && 3, and it evaluates to false.
5. The assertion in the jump method will not fail under any circumstances Here's the interesting one. This, however, is false. It could be true, however, if we could assume that the down method were not called elsewhere. Because the jump method is synchronized, we know only one thread of execution could hold a lock at any time until the method exited; however, the down() is public and may be called in other code.
I think the question would be more interesting if both the up() and down() methods are private to the class, jump() is not synchronized, and the class otherwise exists as written.